Beagle made his NHL debut for the Capitals on February 11, 2009, during a 5–4 shootout loss to the New York Rangers. He registered three shots on goal. Beagle was recalled from the Hershey Bears due to an injury suffered by Alexander Semin in practice. On November 17, 2009, Beagle recorded his first NHL point, an assist on Matt Bradley's game winning goal in the team's 4-2 win over the New York Rangers, and on November 23, he scored his first NHL goal, an unassisted tally against the Ottawa Senators.

Beagle re-signed with the Capitals to a two-year contract on July 15, 2010.